1. Field of the Invention
The present invention relates to a method for forming a membrane electrode diffusion assembly for use in an ion exchange membrane fuel cell.
2. Description of the Prior Art
The operation of fuel cells are well known. In this regard, a fuel cell generates electricity from a fuel source, such as hydrogen gas, and an oxidant such as oxygen or air. The resulting chemical reaction does not result in a burning of the fuel, therefore the thermodynamic limits on the efficiency of such a chemical reaction are much greater than conventional power generation processes. In a proton exchange membrane fuel cell the fuel gas (hydrogen) is ionized on one electrode, and the hydrogen ions diffuse across the membrane to recombine with oxygen ions on the cathode. The resulting byproduct of the reaction is water and the production of an electrical current.
In U.S. Pat. No. 6,030,718, the teachings of which are incorporated by reference herein, a proton exchange membrane fuel cell power system is disclosed and which includes discrete and novel proton exchange membrane fuel cell modules which are self humidifying and which employ a membrane electrode diffusion assembly which provides increased reliability and other advantages not possible heretofore with respect to fuel cell designs which have been primarily directed to stack-type arrangements. While this prior art patent discloses a method of producing a suitable membrane electrode diffusion assembly which operates with a great deal of success, the inventors have endeavored to improve upon this inventive concept by focusing further investigation on a method of manufacturing a membrane electrode diffusion assembly which increases the performance, and versatility of same and which further may be utilized in a modular design such as disclosed in this previous patent, or which may be also utilized in more traditional stack-type arrangements.
Accordingly, a method for forming a membrane electrode diffusion assembly for use in an ion exchange membrane fuel cell which achieves the benefits to be derived from the aforementioned teaching is the subject matter of the present invention.
One aspect of the present invention is to provide a method for forming a membrane electrode diffusion assembly for use in an ion exchange membrane fuel cell which includes providing an ion conducting electrolyte membrane having opposite sides; and applying a first diffusion layer to one of the opposite sides of the ion conducting electrolyte membrane by the application of force sufficient to fabricate a resulting membrane electrode diffusion assembly which has an optimal operational temperature range when utilized in an ion exchange membrane fuel cell of less than about 95 degrees C.
Another aspect of the present invention relates to a method for forming a membrane electrode diffusion assembly for use in an ion exchange membrane fuel cell which includes providing an ion conducting electrolyte membrane having opposite anode and cathode sides; affixing an anode and cathode electrode on the respective anode and cathode sides; positioning a first diffusion layer on one of the anode and/or cathode sides of the ion conducting electrolyte membrane and in covering relation over the respective anode and/or cathode electrode; and applying a force of at least about 400 pounds to about 10,000 pounds per square inch to the first diffusion layer to affix the first diffusion layer on the ion conducting electrolyte membrane to form a resulting membrane electrode diffusion assembly.
Yet further, another aspect of the present invention relates to a method of forming a membrane electrode diffusion assembly for use in an ion exchange membrane fuel cell, and which includes, first, providing an ion conducting electrolyte membrane having opposite anode and cathode sides; second, providing anode and cathode electrodes which are individually affixed on and located at least in partial covering relation relative to the respective anode and cathode sides of the electrolyte membrane; third, providing a first diffusion layer comprising carbon and a fluropolymer, and then heating the first diffusion layer to a temperature of about 100 degrees C. to about 500 degrees C. for a predetermined period of time in an oxygen-containing environment; fourth, affixing the previously heated first diffusion layer in at least partial covering relation relative to each of the anode and cathode electrodes by the application of pressure in the amount of about 400 pounds to about 10,000 pounds per square inch of surface area of the first diffusion layer; providing a permeable substrate having a predetermined thickness dimension and opposite sides; preparing a slurry comprising at least about 20% to about 90% by weight of a particulate carbon and a hydrophobic binding resin dispersed in a water solution which may include surfactant, and applying the slurry to coat one of the sides of the permeable substrate; air drying the coated side of the porous substrate, and after the step of air drying the coated side, applying additional coats of the slurry, each separated by the aforementioned air drying step, to form a second diffusion layer having a resulting hydrophobic gradient; and positioning the second diffusion layer in juxtaposed covering relation relative to the first diffusion layer.
These and other aspects of the present invention will be discussed in further detail hereinafter.